1. Field of the Invention
This invention relates to a liquid crystal display cell having a liquid crystal layer switchable between two optically distinguishable states, wherein the liquid crystal layer is contained between two plane-parallel support plates separated within a predeterined range by spacers.
2. Description of the Prior Art
In a liquid crystal cell the separation between the two support plates, which essentially determines the thickness of the liquid crystal layer, should be as constant as possible over the entire area of the cell. One way to achieve a constant separation is through the introduction of spacers between the support plates.
Liquid crystal cells are known which have glass beads (DE-AS Nos. 28 15 405), glass fibers (GB No. 2 050 637A) or carbon fibers (CH No. 634 422) as spacers.
Spacers composed of electrically conductive material serve, aside from their function as spacers, to make contact bridges between the electrode layers of the two support plates. These spacers are generally distributed in the border, outside of the liquid crystal liquid.
When liquid crystal cells provided with the known spacers are exposed to extreme temperatures (-30.degree. C., +80.degree. C.) or to high relative humidity (90%) numerous defects occur. Low-pressure bubbles, known as vacuoles, appear in the liquid crystal layer at low temperatures. These vacuoles are caused by the differences in the thermal expansion coefficients of the liquid crystal layer and the other cell materials, such as the spacers. At high temperatures and high relative humidities defects appear which are dependent on corrosion. The border, which is also usually the seal, swells and the electrically conducting spacers distributed in the border thereby lose contact with the electrode layers. Contact interruptions are the result. If the liquid crystal cell is operated in transmission with a dark background, then glass spacers inside the liquid crystal layer become visible as luminous bright points and increase the overall brightness of the background. This leads to a poor contrast. Glass spacers in colored liquid crystal layers are especially disturbing because glass that is only a few .mu.m thick cannot be colored intensely enough. Reducing the number of glass spacers in the liquid crystal layer causes them to shatter under the pressure required for the manufacture of the liquid crystal cell.